Update task instructions from old format to match English source:
- Old: "Add <kbd>padding: 1rem</kbd> to <kbd>.box</kbd>"
- New: "Set <kbd>padding</kbd> to <kbd>1rem</kbd>"
Removes redundant class name references since codePrefix shows the selector.
Affected languages: ar, es, pl, uk
- Hello World lesson now styles plain text (no h1 required)
- Added syntax examples to CSS Variables, calc(), Media Queries, Flexbox, Grid
- Added goodbye/offboarding module with contribution encouragement
- Fixed validation in welcome lesson (Hello World instead of Hello)
- Replaced 'quoted text' with <code>quoted text</code> in all task descriptions
- Added syntax examples to Transitions and Keyframes lessons
- Updated all language versions (en, de, pl, es, ar, uk)
- Create lesson directories and copy English lessons as templates
- Add full UI translations for pl, es, ar, uk languages
- Update lessons.js with module stores for all new languages
- Implement language cycling (en → de → pl → es → ar → uk → en)
- Fix playground mode detection (lesson.mode takes precedence)
